Allison Transmission and Tow/Haul Mode

[CT_496]

Does anyone else use the tow haul mode when empty?  I do occasionally on slow backroads to prevent the trans from shifting up into overdrive.

 

When I do, I've noticed that I have a momemtary loss of power while accellerating (moderate to heavy throttle) in 2nd gear.  I get this loss prior to the trans shifting to 3rd.  I can feel the power loss and notice loss of rpm on the tach then it picks back up and finally shifts to 3rd.  One dealer told me that I should not use tow/haul when empty another one flashed the computer and said it was fixed but it wasn't.  I've also noticed some pinging in 3rd when going up a hill and leaning into the throttle.

 

Anyone else have these problems and been able to get them fixed?

[Roofer]

My guess is what you are feeling is torque management from the Allison.

[Woody1]

found this on Allison website for you:

Q. Tow/Haul vs. Normal Mode - If I use use Tow/Haul without a trailer, is that a problem? And vice versa?  

 A. T/H can be used at any time, even when not towing. Some drivers may not like the T/H shift characteristics when the vehicle is lightly loaded, and thus normal mode would be selected. When not heavily loaded, some drivers switch from Normal to T/H mode during closed throttle downshifts from highway speeds to help slow the vehicle and then switch back to Normal mode after they've stopped. If the driver chooses not to use T/H when towing or heavily loaded, he/she can expect to see higher transmission sump temperatures, more wear and tear on the brake system, and increased shift cycling.

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Q. Tow/Haul vs. Normal Mode - What's the difference between Tow Haul and Normal Mode?  

 A. Tow/Haul (T/H) shift mode significantly changes the transmission's shift pattern to reduce shift cycling and to deliver better performance, control, and cooling when towing/hauling heavy loads. For instance:

 

Upshift points are raised at light to mid throttle position to use more of the engine's available power for accelerating.Downshift points are raised to enhance engine braking to help slow the vehicle.

During deceleration, the torque converter clutch (TCC) remains applied at closed throttle to much lower vehicle speeds to significantly improve the effect of engine braking.

During acceleration, the TCC is applied in 2nd range and remains applied in 3rd, 4th, and 5th. This improves the drivetrain efficiency and significantly lowers transmission sump temperature when towing heavy loads. In Normal mode, TCC generally applies only in higher ranges and is dependent on throttle position.

 

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Q. Tow/Haul vs. Normal Mode - When should I use Tow/Haul?  

 A. T/H mode is recommended whenever you are towing or the truck is heavily loaded, for all the reasons noted in the above question.